Member for semiconductor device using an aluminum nitride substrate material, and method of manufacturing the same

ABSTRACT

A highly reliable member for a semiconductor device, in which a high melting point metallizing layer, which consists mainly of a high melting point metal such as W and/or Mo, and an intervening metal layer, which has a melting point of not greater than 1,000° C. and consists mainly of at least one selected from among Ni, Cu and Fe, are provided on an AlN substrate material in this order on the AlN substrate material, and a conductor layer consisting mainly of copper is directly bonded to the intervening metal layer without intervention of a solder material layer. A semiconductor element or the like is mounted on the member for a semiconductor device, thereby fabricating a semiconductor device. The high melting point metallizing layer is formed on an aluminum nitride substrate by post-fire or co-fire metallization.

CROSS REFERENCE TO RELEASED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/412,012, filed Oct. 4, 1999, now abandoned which is adivision of U.S. patent application Ser. No. 08/792,147 filed Jan. 31,1997, now U.S. Pat. No. 5,998,043.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a member for a semiconductor device, inwhich a conductor layer consisting mainly of copper is bonded to analuminum nitride substrate material, a method of manufacturing such amember for a semiconductor device, and a semiconductor device whichemploys such a members.

2. Description of the Prior Art

Conventionally, alumina (Al₂O₃) has widely been used as an insulatingsubstrate material for a semiconductor package, and a member in which ametallized circuit consisting mainly of tungsten is formed on theinsulating substrate material in a multilayer structure has been used asa circuit board for a semiconductor IC. Alumina is superior inelectrical insulation and mechanical strength, but its thermalconductivity is as small as approximately 17 W/m.K and its heatdissipation property is inferior. Alumina is, therefore, inappropriateto a circuit board on which to mount a high-capacity semiconductor IC.

In contrast, aluminum nitride (AlN) has recently been spotlighted as asubstrate material for a circuit board because of its electricalinsulation and mechanical strength approximately equivalent to those ofalumina, its light weight and its high thermal conductivity exceeding100 W/m·K. In addition, aluminum nitride exhibits a mean coefficient ofthermal expansion as small as 5.5×10⁻⁶° C. in the temperature range offrom the room temperature to the silver-soldering temperature(approximately 800° C.), so that aluminum nitride exhibits superiorbondability and compatibility with an Si semiconductor chip (which has acoefficient of thermal expansion of 4.0×10⁻⁶/(° C.). However, aluminumnitride is poor in bondability with Kovar (having a coefficient ofthermal expansion of 10×10⁶/° C.) and a 42 alloy (having a coefficientof thermal expansion of 11×10⁻⁶/° C.) which are used for a packagematerial or a through lead to a circuit board.

It is generally known that various intervening layers are formed betweennitride ceramic and metal so that the nitride ceramic and the metal arebonded to each other. For example, Japanese Patent Publication No.2-34908 (1990) states that a layer made of a low-elastic-modulus metaland/or a metal having malleability and ductility, a layer made of abrittle material and a layer made of a material having a low coefficientof thermal expansion are formed as intervening layers in multilayer inthis order from the ceramic side. However, bonding which uses thesekinds of multiple intervening layers easily lowers the thermalconductivity by the multiple intervening layers provided for bondingpurpose, and the application of such bonding to an aluminum nitride heatsink board is limited practically.

For this reason, it has been a common practice to form a metallizinglayer of W, Mo or the like on the surface of an aluminum nitridesubstrate material and bond the aluminum nitride substrate material to ametal member such as a lead frame or a package by silver-soldering viathe metallizing layer. For example, Japanese Patent Laid-Open No.63-269950 (1988) discloses the art of forming a W metallizing layer onan aluminum nitride substrate material and bonding a lead frame made ofoxygen free copper having a high heat conductivity and a high thermalshock absorbing property (refer to FIGS. 1 and 2 of Japanese PatentLaid-Open No. 63-289950) to the W metallizing layer by silver-soldering.In this art, if necessary, an Ni layer for improving the wettability isformed on each of the W metallizing layer and the oxygen free copperlead frame, and both are bonded to each other by silver-soldering.

In accordance with the aforesaid method of bonding the oxygen freecopper lead frame to the aluminum nitride substrate material via themetallizing layer, thermal stress due to heating during silver-solderingis greatly reduced compared to ordinary lead frames using Kovar or thelike, so that the bonding strength which lowers in the case of Kovardoes not lower. However, the aforesaid method involves the problem thatthe shape of the lead frame is difficult to maintain because oxygen freecopper is a soft material. In addition, if a copper-based member isjoined to an aluminum nitride substrate material via a silver-solderlayer in the above-described manner, a large thermal stress action dueto the silver-soldering occurs owing to the difference in thermalexpansion between the silver-solder and the aluminum nitride, so thatbreakage or deformation, such as cracking or warp, easily occurs in thealuminum nitride substrate material after the cooling. This leads to theproblem that a special expensive silver-solder material which issilver-rich and soft needs to be employed to lower the cooling stress,or strict control for a small-amount region is needed to make thesilver-solder layer thinner.

Under the circumstances, investigations have been made into variousmethods of bonding a metal member which is a conductor to an aluminumnitride substrate material without forming an intervening layer ofsolder material such as silver-solder. One method is a so-called DBC(direct bonding copper) method which does not use a W metallizing layernor a solder layer to bond copper as a metal member to an aluminumnitride substrate material.

For example, Japanese Patent Laid-Open No. 59-40404 (1984) discloses amethod which includes the steps of forming on the surface of an aluminumnitride substrate material either a layer of an oxide of the aluminumnitride substrate material itself or a binding layer made of an oxide ofaluminum, a rare earth element or an alkaline earth element which areused as sintering aids for the preparation of a sintered body ofaluminum nitride, preparing, as a counterpart to be bonded to thealuminum nitride substrate material, a metal material which contains alittle amount of a binder of such oxide (which may contain oxygen alone)or has such layers formed on its surface in advance, and directlybonding the aluminum nitride substrate material and the metal materialby using the affinity between the binding layers on these materials. Forexample, if the metal material is made of copper, it is bonded to thealuminum nitride substrate material having the oxide layer thereon,using the copper oxide formed on its surface, by subjecting the materialto heat treatment in the temperature range of from the eutectictemperature of the copper oxide and copper to the melting point ofcopper.

A similar method is disclosed in Japanese Patent Laid-Open No. 60-32343(1985). This method is a bonding method in which a thin copper-alloyeutectic layer containing an active metal (such as Ti, Zr or Hf) isintervened between an aluminum nitride substrate material and a copperheat sink board. Another DBC method is described in “ElectronicsCeramics”, the November issue, 1988, pp. 17 to 21. In this method, athin aluminum oxide layer of up to several microns is first formed onthe surface of an aluminum nitride substrate material and then copper isbonded to the thin aluminum oxide layer via a Cu₂O—Cu eutectic layer.

However, in any of the above-described methods of bonding copper toaluminum nitride by using an eutectic region of a copper oxide andcopper, the variation of the bonding strength easily becomes greatunless the thickness of the oxide layer on the aluminum nitride iscontrolled within a narrow range, as illustrated in FIG. 4 of theabove-cited report of “Electronic Ceramics”. In addition, in thesemethods, since an intervening layer made of aluminum oxide and a copperoxide eutectic component formed between an aluminum nitride substratematerial and a copper member is thin, breakage or deformation such ascracking or warp easily occurs in the substrate material owing to thedifference in thermal expansion between copper and aluminum nitride. Inaddition, it is necessary to create a special oxygen partial-pressureatmosphere for eutectic bonding of copper and copper oxide at around1,000° C. Since the surface of the copper member is oxidized by thespecial oxygen partial-pressure atmosphere, an extra step such assurface polishing is needed before the copper member is subjected tosolder-bonding. When the copper member is mounted on the aluminumnitride substrate material, it is necessary to carry out thetime-consuming step of performing positioning for defining anon-mounting portion, and forming with good reproducibility the boundarybetween the copper member and a fuse-contact portion on which to mountthe copper member.

In the method using an active metal as described in Japanese PatentLaid-Open No. 60-32343 (1985), an expensive active drive solder materialis needed, and a high vacuum of not greater than 10⁻⁴ Torr is neededduring soldering. In many cases of soldering in nitrogen gas, it is alsonecessary to prepare a special metal soldering material containing,e.g., a large amount of Ti in advance. Furthermore, if such an activemetal solder material is employed, voids are easily produced in theinterface between aluminum nitride and the active metal solder material,so that cracking easily occurs therein. Thermal resistance may alsoincrease because of the presence of the soldering material.

SUMMARY OF THE INVENTION

In consideration of the above-described problems, an object of thepresent invention is to provide a member for a semiconductor device,which has a bonding structure for ensuring high-strength bonding betweenan aluminum nitride substrate material and a conductor layer so that ametal member can be mounted to an aluminum nitride substrate materialwith high reliability in a semiconductor device which uses aluminumnitride for a substrate material, particularly in a connection structurefor a high-power module in order to form a conductor layer consistingmainly of copper on the aluminum nitride substrate material, bypreventing the substrate material from suffering the aforesaid damageduring soldering to the W metallizing layer, preventing the substratematerial from suffering breakage or deformation when a copper conductorlayer is directly bonded to the substrate material by using theaforesaid copper oxide eutectic, preventing breakage of the member dueto deformation (deflection) which occurs during the step of fixing themember to a semiconductor device after bonding, preventing increases ofthe material and working costs required for soldering and mounting.

To achieve the above object, the present invention provides a member fora semiconductor device in which a high melting point metallizing layer,which consists mainly of a high melting point metal, and an interveningmetal layer, which has a melting point of not greater than 1,000° C. andconsists mainly of at least one selected from the group consisting ofnickel, copper and iron, are provided on an aluminum nitride substratematerial in this order from the aluminum nitride substrate material, anda conductor layer consisting mainly of copper is directly bonded as acircuit layer to the intervening metal layer, without forming anintervening solder layer.

Specifically, the present invention relates to a member for asemiconductor device, in which a conductor layer consisting mainly ofcopper which is widely used for use as high-power module, is provided onan aluminum nitride substrate material which is superior in heatdissipation property. In accordance with the present invention, it ispossible to provide a semiconductor device such as a high power moduleby die-bonding a semiconductor device to the conductor layer of themember.

The reliability of conventional direct bonding of a copper heat sinkboard and an aluminum nitride substrate material via an oxide layer oran activated metal solder layer is extremely low. For example, crackingor warp of the aluminum nitride substrate material or separation of thecopper heat sink board is caused by thermal stress which occurs duringmanufacture or use owing to the difference in thermal expansion betweenthe copper heat sink board and the aluminum nitride substrate material.In addition, in the above-described copper eutectic bonding method usingan intervening oxide layer, a groove may be provided in the bondinginterface of a copper sheet as a conductor layer and the aluminumnitride substrate material so as to facilitate the forming of the oxidelayer on the bonding interface. However, after the bonding, such groovemay be left as a gap which lowers the strength. The bonding method usingactive metal solder may involve a positional deviation during bonding orallow an etchant to enter the bonding interface during etching in thecircuit forming step. As a result, a space is produced between thealuminum nitride substrate material and the copper conductor layer,thereby also lowering the bonding strength.

To solve the above-described problems and improve the reliability to agreat extent, the present invention provides a structure in which a highmelting point metallizing layer and an intervening metal layer which hasa melting point of not greater than 1,000° C. and consists mainly of atleast one selected from the group consisting of nickel, copper and ironare formed between an aluminum nitride substrate material and aconductor layer consisting mainly of copper, without intervention of asolder layer between the intervening metal layer and the conductorlayer. The role of the high melting point metallizing layer is notlimited to only plating precipitation, solder-flow stabilization andgeneral surface metallization for circuit formation or the like. Thehigh melting point metallizing layer having a high Young's modulusabsorbs the thermal stress due to the difference in thermal expansionbetween the conductor layer consisting mainly of copper and the aluminumnitride substrate material, thereby relaxing the thermal stress whichadversely affects the aluminum nitride substrate material. The role ofthe intervening metal layer is to melt below 1,000° C. so as to bond thehigh melting point metallizing layer to the conductor layer whichconsists mainly of copper. As the material of the intervening metallayer, a material of low hardness or a material which can readily bereduced in thickness is preferable so that the thermal stress generatedcan be decreased compared to general silver solder or activated metalsolder.

It is particularly preferable that the length and width in the planedirection of the conductor layer be shorter than those of the highmelting point metallizing layer and the intervening metal layer by notless than 0.05 mm so as to prevent a discharge phenomenon from occurringbetween the copper sheet, which is the conductor layer, and the aluminumnitride substrate material and to provide a far more reliable member fora semiconductor device. Furthermore, the end shape of the conductorlayer formed of the copper sheet is such that the angle formed by theside face of the conductor layer and the bonding interface between theconductor layer and the intervening metal layer is not greater than 80°,whereas the angle formed by the, upper surface and the side face of theconductor layer is not less than 80°. Accordingly, the dischargephenomenon preventing effect is improved to a further extent. The endsurface of the conductor layer may be curved outwardly or inwardly incross section. Incidentally, the end surface of the conductor layer ispreferably a surface which is as smooth as possible, and more preferablythe Rmax of the end surface is not greater than 20 μm so that adischarge phenomenon can be prevented from occurring between theconductor layer and the aluminum nitride substrate material. For thesame reason, it is preferable that none of the corners or the edges ofthe conductor layer have a projection such as a burr, and, moreparticularly, small rounded surfaces are provided on the respectivecorners or edges of the conductor layer.

A sintered body of aluminum nitride which Is employed as an aluminumnitride substrate material may contain generally known additives such asa rare earth element compound such as Y₂O₃, an alkaline earth elementcompound such as CaO, and, if necessary, a transition element compoundsuch as TiN. The sintered body has a relative density of not less than95%, preferably not less than 98%. The thermal conductivity of thesintered body is preferably not less than 100 W/m·K, more preferably notless than 150 W/m·K. Incidentally, a thin layer containing oxygen maypreviously be formed on the surface of the aluminum nitride substratematerial on which to form a metallizing layer. This thin layer is mainlyintended to accelerate the bonding of the aluminum nitride substratematerial and the high melting point metallizing layer, and contains, forexample, Al, Si, a rare earth element, an alkaline earth element, andoxygen.

The high melting point metallizing layer consists mainly of a highmelting point metal such as W, Mo, Ta, Ti and/or Zr. In order to improveits bondability with aluminum nitride, the high melting pointmetallizing layer may contain a glass frit which contains the aforesaidelements added to the sintered body, such as a rare earth element, analkaline earth element, Si, Al and other transition elements. It isdesirable that the thickness of the high melting point metallizing layerbe 3-50 μm.

The intervening metal layer provided on the high melting pointmetallizing layer is preferably a layer of a composition having amelting point of not greater than 1,000° C. and comprising as a maincomponent at least one selected from the group consisting of Ni, Fc andCu. Two or more intervening metal layers may be formed. The thickness ofthis intervening metal layer is preferably 2-40 μm, and more preferably5-20 μm. An Ni—P composition is the one suited to the intervening metallayer, and a structure in which a layer of Ni—P composition is formed ona layer of Ni—B composition is particularly preferable.

The material of the conductor layer which consists mainly of copper andwhich is bonded to the aluminum nitride substrate material via theabove-described two layers may be copper such as oxygen free copper ortough pitch copper, a copper alloy such as a copper-molybdenum alloy, acopper-tungsten alloy or a copper-molybdenum-tungsten alloy, or a cladmaterial such as copper-molybdenum-copper having both a high electricalconductivity and a low coefficient of thermal expansion. A metal memberwhich is disposed around aluminum nitride in a semiconductor device, andmade of, for example, an Fe—Ni—Co alloy such as Kovar, an Fe—Ni alloysuch as a 42 alloy, Ni, an Ni alloy, Cu, a Cu alloy, W, Mo, a W alloy,or an Mo alloy may be directly or indirectly bonded to the conductorlayer, as required.

Methods of manufacturing a member for a semiconductor device accordingto the present invention will be described below. First, a high meltingpoint metallizing layer is formed on the above-described aluminumnitride substrate material. One of the methods of forming the highmelting point metallizing layer includes the steps of preparing asintered body of aluminum nitride in advance, subjecting the sinteredbody to the above-described surface treatment (forming anoxygen-containing thin layer) if necessary, coating the resultantsintered body with a paste, which comprises, as a main component, ametal selected from among the aforesaid high melting point metals, amixture thereof, or a mixture of such metal or metals and the aforesaidglass frit, is mixed with an organic binder (viscous material) and anorganic solvent (viscosity modifier of the binder), for example, byprinting to form a layer, preferably with a thickness of 5-60 μm, andfiring the layer. This procedure is a so-called post-fire metallizingmethod.

There is another method which includes the steps of adding a formingorganic binder to an aluminum nitride material powder mixture with apredetermined composition, compacting the obtained mixture into acompact, coating the compact with a high melting point metal pastesimilar to the above-described one, and firing the paste and sinteringthe compact at the same time. This method is a so-called co-firemetallizing method. In the case of this method, it is important thathigh melting point metal grains as fine as possible are used for thehigh melting point metal paste and an agent which produces a liquidphase at low temperatures is selected as an additive for acceleration ofsintering of aluminum nitride so that the sintering can be effected bycofiring at the same time at a lower temperature and their shrinkagefactors can be made approximately equal to each other, therebypreventing deformation of the aluminum nitride substrate material duringsintering. In addition, it is expected that since the crystal grains ofthe aluminum nitride substrate material are made fine by sintering atlow temperatures, the strength of the aluminum nitride substratematerial is increased.

After the high melting point metallizing layer has been formed in theabove-described manner, an intervening metal layer having a compositionwhich has a melting point of not greater than 1,000° C. and comprises,as a main component, Ni, Cu and/or Fe is formed. This intervening metallayer may be formed by any of the following methods: (1) forming theintervening metal layer on the bonding interface of the conductor layerconsisting mainly of copper to be bonded to the aluminum nitridesubstrate material; (2) forming the intervening metal layer on the highmelting point metallizing surface of the aluminum nitride substratematerial; and (3) forming the intervening metal layer on both of thehigh melting point metallizing layer formed on the aluminum nitridesubstrate material and the conductor layer comprising copper as a maincomponent. Two or more intervening metal layers of different kinds maybe formed, as required. For example, in a representative example inwhich a nickel-phosphorus layer is formed on the high melting pointmetallizing layer on the aluminum nitride substrate material, after ahigh melting point metallized surface is subjected to nickel-boronplating, nickel-phosphorus plating may be applied to thenickel-boron-plated surface.

After that, the aluminum nitride substrate material and a materialprepared for forming the conductor layer comprising copper as a maincomponent are superposed on each other, with the intervening metal layerformed by any of the above-described methods sandwiched therebetween inwhich the conductor layer is directly bonded as a circuit layer to theintervening metal layer without any solder layer; and the aluminumnitride substrate material and the conductor layer are bonded to eachother by firing in a nitrogen-containing atmosphere at a temperatureless than the melting point of the conductor layer, thus producing amember for a semiconductor device according to the present invention.The strength of the bonded portion of the member for a semiconductordevice according to the present invention is stable at a high peelstrength of not less than 0.5 kg/1 mm.

Incidentally, during the aforesaid sintering for bonding, if necessary,the aluminum nitride substrate material and the conductor layer may betemporarily fixed by using a setting jig made of a refractory materialsuch as a carbon material, an alumina material or an aluminum nitridematerial, and, if further necessary, an appropriate load may be appliedto a set in which both are superposed one on the other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a method of measuring thepeel strength of the bonded portion of a member for a semiconductordevice according to the present invention.

FIG. 2 is a schematic explanatory view showing the end shape of aconductor layer according to the present invention.

FIG. 3 is a partly cutaway, side elevational view schematically showinga semiconductor device of the present Invention which was produced inExamples 3 and 8.

FIG. 4 is a schematic cross-sectional view showing a member for asemiconductor device of the present invention which member was producedin Examples 3 and 8.

FIG. 5 is a schematic cross-sectional view showing a member for asemiconductor device which was produced as a comparative example ofExample 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The reason why the relative density of the aluminum nitride substratematerial used in the present invention is preferably not loss than 95%is that the strength of its sintered body lowers when the relativedensity is less than 95% and if such a sintered body is employed as aproduct, the reliability against thermal shock may become low. Thereason why the thermal conductivity of the aluminum nitride substratematerial is preferably at least 100 W/m·K is that, at a thermalconductivity of less than 100 W/m·K, it is difficult to achieveeffective dissipation of heat generated during the operation of anelement, particularly in the case of a power element.

The composition of the high melting point metallizing layer after tiringpreferably contains a high melting point metal in an amount of not lessthan 80 volume % and the aforesaid type of glass frit in an amount ofnot greater than 20 volume %. If the content of the high melting pointmetal is less than 80 volume % or the content of the glass frit exceeds20 volume %, the thermal conductivity of the high melting pointmetallizing layer may lower. It is desirable to control the thickness ofthe high melting point metallizing layer after firing within 3-50 μm. Ifsuch thickness is less than 3 μm, it may be impossible to provide asatisfactory mechanical adhesion between the high melting pointmetallizing layer and the aluminum nitride substrate material, whereasit the thickness exceeds 50 μm, the warp of the aluminum nitridesubstrate material tends to increase after the formation of theintervening metal layer.

The intervening metal layer has a composition which consists mainly ofNi, Fe and/or Cu and has a melting point of not greater than 1,000° C.,and it is particularly desirable to use a nickel-phosphorus compositionas described previously. The reason why the nickel-phosphorusintervening metal layer is preferable in the present invention is asfollows. A eutectic Ni—P is formed at the interface at a temperaturelower than the melting temperature of Ni itself and the reaction isaccelerated, so that since Ni melts at this time, a good bonding can beprovided between the conductor layer and W or the like of the highmelting point metallizing layer.

The thickness of the intervening metal layer is preferably 2-40 μmimmediately after sintering. If the thickness is less than 2 μm, asufficient liquid phase for bonding is not obtained and an unboundedportion easily occur, so that thermal resistance may increase and stressdue to the difference in heat shrinkage between the metallic portion ofthe copper conductor layer and AlN may concentrate. If the thicknessexceeds 40 μm, since Ni—P is a metal having a high Young's modulus, theabsolute value of the difference in thermal stress between Ni—P and thealuminum nitride substrate material increases as the bonding areabetween Ni—P and the aluminum nitride substrate material increases, sothat an excessive stress is applied to the aluminum nitride substratematerial and the strength thereof may be degraded.

Incidentally, either electrolytic plating or electroless plating may beused as a plating method for forming the intervening metal layer. Asanother method of forming the intervening metal layer, printing, vapordeposition or the like may also be adopted other than the plating. Thethus-formed intervening metal layer is preferably sintered in anon-oxidizing atmosphere.

The bonding of a conductor layer material and the aluminum nitridesubstrate material on which the intervening metal layer has previouslybeen formed on the metallizing layer is carried out at a temperature ofless than the melting point of the conductor layer material in anitrogen-containing atmosphere, without forming a solder layer on theintervening metal layer. It is not preferable that the bondingtemperature be not less than the melting point of the conductor layermaterial, because the desired dimensions of the conductor layer are notobtained after bonding and a predetermined circuit pattern which haspreviously been formed on the conductor layer is damaged, with theresult that the predetermined circuit pattern may be short-circuited.Incidentally, the member for a semiconductor device according to thepresent invention can also be adapted to a high-power module board, forexample, a structure which uses a conductor layer consisting mainly ofaluminum instead of copper.

EXAMPLE 1

An AlN powder of 1.2 μm in mean grain size, Y₂O₃ powder of 0.6 μm inmean grain size, and CaO powder of 0.3 μm in mean grain size wereprepared in weight percentages of 9 wt. %, 1.5 wt. % and 1.5 wt. %,respectively, and the thus-prepared powders were uniformly mixed for 24hours in an ethanol solvent by means of a ball mill. Then, 10 parts byweight of PVB were added to 100 parts by weight of the powder mixture,thus preparing a slurry.

Part of the slurry was spray-dried and then compacted into a plate shapeby a powder compacting press. Then, the compacted product was sinteredat 1,700° C. in a nitrogen atmosphere for 5 hours, thereby preparing aplate sintered body of AlN. One side of the obtained AlN sintered bodywas coated with a paste comprising, as a main component, a W powder of 1μm in mean grain size and containing 5 wt. % of an SiO₂-based frit.After de-gassing, the sintered body was fired at 1,600° C. in a nitrogenatmosphere, thus forming a high melting point metallizing layer (thepost-fire metallizing method).

The remainder of the slurry was formed into a sheet of 1.0 mm thick×100mm wide by a doctor blade method, and then formed into a plate productby blanking. The thus formed plate product was similarly coated with thesame paste above-described, and after de-gassing, the thus-coated plateproduct was fired at 1,700° C. in a nitrogen atmosphere for 5 hours,thereby effecting firing of the paste and sintering of aluminum nitrideat the same time (the co-fire metallizing method).

Metallized AlN substrate materials of the kinds shown in Table 1, eachof which had a W high melting point metallizing layer, were produced byeither of the above-described methods. Incidentally, the materialsproduced by the post-fire metallizing method and those produced by theco-fire metallizing method were of the same shape. The sintered aluminumnitride exhibited a density of 99% and no voids were observed in itssurface, and its thermal conductivity ranged from 150 W/m·K to 160W/m·K.

TABLE 1 Size of Metallized AlN Thickness of Substrate MaterialMetallizing Length Width Thickness layer Sample (mm) (mm) (mm) (μm) 1 2525 0.635 2 2 25 25 0.635 3 3 25 25 0.635 5 4 25 25 0.635 10 5 25 250.635 20 6 25 25 0.635 50 7 25 25 0.635 60 8 25 25 0.635 70 9 50 500.635 5 10 50 50 0.635 10 11 50 50 0.635 15 12 50 50 0.635 20 13 100 1000.5 5 14 100 100 0.5 10 15 100 100 0.5 15 16 100 100 0.5 20

Ten samples were selected from each of the sample groups, and after thehigh melting point metallized surfaces of the selected samples wereplated with Ni—P, the plated samples were held at 600° C. for 30 minutesin a nitrogen atmosphere, thus sintering the Ni—P plating layers. Anyabnormality such as blister or peeling was not observed in any of theobtained intervening metal layers, and the plating thickness of any ofthe samples was in the range of 6±0.3 μm.

As a conductor layer, an electrolytic copper material of JIS C1020 whichwas 1 mm thick and equal in length and width to the AlN substratematerial was placed on each of the samples, and the samples were placedon a graphite-made setter and were subjected to in-furnace bonding at970° C. for 30 minutes under a no-load condition in a nitrogen gas flow.An area analysis using an ultrasonic flaw detector was made on each ofthe samples after bonding, and no abnormal detect was observed. Inaddition, the cross section of each of the samples after bonding wasobserved with an SEM (scanning electron microscope) (magnification:×1,000), defects such as cracks or pin holes were not observed at theinterface.

The peel strength and the warp of each of the obtained samples weremeasured, and the results were classified into a data group based on thepost-fire metallizing method and a data group based on the co-firemetallizing method. The respective data groups are shown in Tables 2 and3. The warp was obtained by placing each of the samples on a surfaceplate with its conductor layer faced up, measuring the differencebetween the maximum height and the minimum height from the surface plateof each of the samples on a diagonal line thereof, and converting thedifference into a value per millimeter of the diagonal. The peelstrength of the bonded portion of each of the samples was measured by,as shown in FIG. 1, bonding a conductor layer 4 of 0.1 mm thick×4.0 mmwide to an intervening metal layer 3 provided on a nigh melting pointmetallizing layer 2 of an AlN substrate material 1, in such a manner asto make the length “1” equal to 3 mm, and then pulling a grip portion 4a projecting perpendicularly upwardly from one end of the conductorlayer 4, in the upward direction at a speed of 20 mm/min.

TABLE 2 Post-Fire Metallizing Method Peel Strength Warp Sample (kg/1 mm)(μm/mm) 1 0.5-0.6 0.2-0.3 2 0.7-1.2 0.3-0.4 3 1.4-1.8 0.6-0.8 4 1.5-1.91.0-1.2 5 1.5-1.7 1.8-2.1 6 1.4-1.9 2.0-2.1 7 1.6-1.8 2.3-2.4 8 1.5-1.62.4-2.6 9 1.3-1.8 0.7-0.9 10 1.7-2.0 1.1-1.3 11 1.6-1.8 1.7-2.1 121.7-1.9 2.1-2.3 13 1.2-1.8 0.6-0.9 14 1.6-2.1 1.1-1.3 15 1.7-2.0 1.9-2.216 1.7-1.9 2.1-2.2

TABLE 3 Co-Fire Metallizing Method Peel Strength Warp Sample (kg/1 mm)(μm/mm) 1 0.5-0.6 0.4-0.5 2 0.8-1.4 0.4-0.5 3 2.6-3.2 0.6-0.8 4 2.8-3.21.1-1.3 5 3.1-3.4 1.7-2.0 6 3.3-3.5 2.2-2.4 7 3.4-3.8 2.4-2.6 8 3.0-3.52.5-2.8 9 2.8-3.8 0.8-1.0 10 2.8-3.2 1.1-1.4 11 3.2-3.5 1.8-2.2 123.1-3.9 2.2-2.3 13 2.8-3.4 0.7-1.0 14 3.2-3.4 1.2-1.4 15 3.4-3.5 2.0-2.216 3.0-3.8 2.1-2.2

As can be seen from the above results, according to the structure of thepresent invention, even a large-size substrate material of 25 mm long×25mm wide only exhibited practically allowable levels of a warp ofapproximately 3.0 μm/mm at the most and a peel strength of approximately0.5 kg/mm at a minimum. In addition, it can be seen that when thethickness of the high melting point metallizing layer was 3 μm to 50 μm,the peel strength exceeded 0.5 kg/1 mm and the warp became less than 3.0μm/mm, so that a high melting point metallizing layer could be obtainedat a practically sufficiently stable level.

From the data of Tables 2 and 3, the following points are apparent whenthe post-fire metallizing method and the co-fire metallizing method arecompared. The peel strengths of the co-fired metallized products areapproximately twice as high as those of the post-fired metallizedproducts. This is because, unlike the post-fire metallizing method inwhich only W on the sintered body is fired, in the co-fire metallizingmethod in which W is fired at the same time of the sintering of acompacted product, W and AlN are firmly bonded to each other by aso-called anchor effect and W itself becomes dense.

COMPARATIVE EXAMPLE

Using AlN substrate materials metallized by co-fire metallization havingthe same sizes as those of samples 4, 10 and 14 of Example 1 andnon-metallized AlN substrate materials prepared for the post-firemetallization of the samples 4, 10 and 14, a Cu-made metal member havingthe same length and width as those of Example 1 was bonded to each ofthe metallized or non-metallized AlN substrate materials by aconventional known method, i.e., silver soldering or copper eutecticbonding. Thus, 10 samples were prepared for each of the AlN substratematerials.

For silver soldering, a 13 Ag-8 silver solder material (Ag 78%-Cu 22%)conforming to the Japanese Industrial standards was employed as a soldermaterial. The same metallized AlN substrate materials and Cu-made metalmembers as those used in Example 1 were bonded to each other by holdingthem at 780° C. for 30 minutes under a no-load condition in a nitrogenatmosphere. In copper eutectic bonding, the non-metallized AlN substratematerials having the same sizes as those of the respective samples 4, 10and 14 were surface-oxidized at 1,100° C. in air to form Al₂O₃ layers onthe respective AlN substrate materials, and Cu-made metal members, eachof which had the same length and width as those of the AlN substratematerial, and had an oxidized surface of Cu₂O and a thickness of 0.3 mm,were placed on and bonded to the respective AlN substrate materialshaving the Al₂O₃ layers formed on their surfaces.

In the observation of the appearance of each bonding interface,particularly in each of the sample 10 of 50 mm×50 mm and the sample 14of 100 mm×100 mm, small cracks were observed in its ceramic portion, andsmall voids were observed in the portion between the solder materiallayer and the Cu-made metal member and in the portion between the Cueutectic layer and the Cu-made metal member, in the bonding layer.Incidentally, although abnormal defects such as cracks or voids were notexternally observed in the sample 4 of 25 mm×25 mm, approximately 30% ofdefective portions (vacant portions) were detected even in the sample of25 mm×25 mm by an area analysis using a ultrasonic flaw detector.

The peel strength and the warp of each of the aforesaid samples weremeasured similarly to Example 1, and the results are shown in Table 4.Incidentally, in the case of copper eutectic bonding, the peel strengthand the warp were measured by similarly pulling up the portion of thecopper-made metal member which was bonded directly to the AlN substratematerial without using any intervening layer. Furthermore, each of thesamples was subjected to a heating-cooling heat cycle (thermal shock)test in which each sample was subjected to 10-cycles of repetition of 0°C.×15 min→100° C.×15 min. The results are also shown In Table 4. InTable 4, the term “cracking” means that the AlN substrate materialcracked in its thickness direction, and the term “peeling” means thatthe bonded portion peeled off near the interface between the AlNsubstrate material and the Cu-made metal member. In the case of each ofthe aforesaid 3 samples of the present invention in which a Cu-mademetal member which had the same shape as the aforesaid one and was notsubjected to oxidation treatment wad bonded to the Ni—P interveninglayer of the AlN substrate material prepared by the co-fire metallizingmethod, cracks such as those observed in the comparative example werenot at all observed after the thermal shock test.

TABLE 4 Peel Evaluation after Bonding Strength Warp 10 Cycles of SampleSample Size Method (kg/ 1 mm) (μm/mm) Thermal Shock  4-a 25 mm × 25 mmAg Solder 1.2-2.0 1.3-1.8 Cracking 10-a 50 mm × 50 mm Ag Solder 1.2-2.02.3-3.0 Cracking 14-a 100 mm × 100 mm Ag Solder Unmeasureable 3.4-4.6Cracking  4-b 25 mm × 25 mm Cu Eutectic 1.5-2.2 1.4-2.1 Peeling 10-b 50mm × 50 mm Cu Eutectic 1.5-2.2 2.6-3.8 Cracking 14-b 100 mm × 100 mm CuEutectic Unmeasurable 3.6-4.8 Cracking

From the above results, the following points become apparent, bycomparing with the aforesaid products of Example 1 of the presentinvention. Any of the products using Ag soldering or Cu eutectic bondingis broken or undergoes peeling of a bonded portion, owing to thermalshock. This is because thermal stress occurs since the coefficient ofthermal expansion of each of Ag—Cu and Cu is large compared to AlN. Inthe case of Ag soldering and Cu eutectic bonding, the warp after bondingis large, so that a product of not less than 15 mm×15 mm is difficult toproduce. This is because the coefficients of thermal expansion of Agsolder and Cu are large. Incidentally, it is considered that the causeof the fact that Ag-soldering bonding leads to a slightly smaller warpthan that of Cu eutectic bonding is the stress relaxation due to W.

EXAMPLE 2

Metallized AlN substrate materials each having a metallizing layerformed by post-fire metallizing under the same conditions as those ofsample 4 shown in Table 1 of Example 1 were prepared, and an interveningmetal layer having a thickness within 6±0.3 μm was formed on the entiremetallizing layer by Ni—P plating in a manner similar to that used inExample 1. An abnormality such as blister or peeling was not observed inany of the intervening metal layers.

Then, copper materials of JIS C1020 of 0.3 mm in thickness were placedon the surfaces of the respective intervening metal layers, and thesesets were disposed on a graphite-made setter and were subjected toin-furnace bonding at 900° C. for 30 minutes under a no-load conditionin a nitrogen gas flow, thereby forming conductor layers. In this case,the copper materials were changed with respect to the length and widthin the planar direction of each intervening metal layer, as shown inTable 5. Thus, 120 samples were produced for each size of the Cumaterials. Area analysis using an ultrasonic flaw detector was made onthe bonded surfaces of the 120 samples, and no abnormal defect wasobserved. In addition, the cross section of each of 5 samples extractedfrom each sample group after bonding was observed with an SEM (scanningelectron microscope) (magnification: ×1,000), defects such as cracks orpin holes were not observed at their interfaces.

Then, the peel strength and the warp of 15 samples extracted from eachsample group were measured in a method similar to that used in Example1, and it was found out that the peel strength and the warp of each ofthe 15 samples were equivalent to those of the sample 4 shown in Table3. After that, a check was made on the presence or absence ofdegradation in the dielectric strength of each of the remaining 100samples for each group before and after the application of AC 1,000 V×10min. The results are also shown in Table 5. From the results shown inTable 5, it can be seen that the probability of occurrence ofdegradation phenomenon of the dielectric strength is small when theplanar length and width of the conductor layer are equal to or smallerthan the corresponding length and width of the intervening metal layer.It can also be seen that if the differences in length and width betweenthe intervening metal layer and the conductor layer, which are obtainedby subtracting the length and width of the conductor layer from those ofthe intervening metal layer are 0.05 mm or larger, the degradationphenomenon of the dielectric strength does not occur.

TABLE 5 Difference in Length and Width of Intervening Metal Layer Numberof Samples Conductor Layer which Degraded in Lengthwise BreadthwiseDielectric Strength Sample (mm) (mm) among 100 Samples 17 0.25 0.25 0 180.10 0.10 0 19 0.07 0.07 0 20 0.05 0.05 0 21 0 0 0 22 −0.03 −0.03 5 (NoProblem in Practical Use) 23 0.07 −0.03 3 (No Problem in Practical Use)24 −0.03 0.07 3 (No Problem in Practical Use)

EXAMPLE 3

A metallizing layer and an intervening metal layer by nickel-phosphorusplating were formed under the same conditions as described in Example 2,and a conductor layer was formed of a copper material identical to thatof Example 2, under the conditions similar to those of Example 2. Inthis case, as shown in FIG. 2, the planar length and width of theconductor layer 4 were made 0.10 mm shorter than those of theintervening metal layer 3 and all the side faces of this copper materialwere etched so that the angle θ₁ formed by the upper surface 4 ₃ and aside face 4 ₂ of the conductor layer 4 and the angle θ₂ formed by theside face 4 ₂ of the conductor layer 4 and a bonding interface 4 ₃between the conductor layer 4 and the intervening metal layer 3 wereshown in Table 6.

Although an area analysis using an ultrasonic flaw detector was made onall 120 samples for each case prepared in the above-described manner, noabnormal detects were observed, and no defects were observed in 5samples extracted from each sample group even by a cross-sectionobservation similar to that preformed in Example 2. The peel strengthand the warp of each of extracted samples by a method similar that usedin Example 2 were measured, and it was confirmed that the peel strengthand the warp of each sample were equivalent to those or the sample 4shown in Table 3. After that, each of 100 samples was bonded to acopper-made heat sink board by using a eutectic solder, thus preparingsemiconductor device each having the structure shown in FIG. 3.

Specifically, as shown in FIG. 4, the structure of a member 5 formed byeach of the samples was such that a W high melting point metallizinglayer 2, an Ni—P intervening metal layer 3 and a copper conductor layer4 are bonded to each side of the AlN substrate material 1 in multilayerin this order. This member 5 was bonded to a copper-made heat sink board6 by using a eutectic solder 7, and a semiconductor element 8 was bondedto one of the copper conductors 4 by die-bonding and was connected toanother copper conductor 4 via leads 9. Then, as shown in FIG. 3, theobtained product was accommodated into a casing 11 provided withexternal terminals 12 and the casing 11 was filled with a resin fillerlayer 13, thus preparing a semiconductor device.

A voltage is applied to each of the 100 semiconductor devices for eachsample group in which the members were incorporated, under the samecondition as of Example 2, and variations in dielectric strength beforeand after the application of the voltage were measured. The results isshown in Table 6. No degradation in dielectric strength was observedbefore and after the application of the voltage, in any sample in whichthe angle θ₁ (shown in FIG. 2) formed by the upper surface 4 ₁ and theside face 4 ₂ of the conductor layer 4 was not less than 80° and theangle θ₂ (shown in FIG. 2) formed by the side face 4 ₂ of the conductorlayer 4 and the bonding interface 4 ₃ between the conductor layer 4 andthe intervening metal layer 3 was not greater than 80°. However, in anysample in which the angle θ₁ was less than 80° and/or the angle θ₃ wasgreater than 80°, degradation in dielectric strength due todeterioration of resin caused by discharge from the conductor layer 4was observed. Incidentally, in any of the samples, no defect due tocracking or warp was observed around the peripheries of the AlNsubstrate material and the conductor layer of the semiconductor deviceafter the application of the voltage.

TABLE 6 Number of Samples which Degraded in Dielectric Strength SampleAngle Θ₁(°) Angle Θ₂(°) among 100 Samples 25 85 75 0 26 100 55 0 27 8585 1 (No Problem in Practical Use) 28 100 85 2 (No Problem in PracticalUse) 29 85 100 1 (No Problem in Practical Use) 30 40 100 1 (No Problemin Practical Use) 31 50 140 1 (No Problem in Practical Use) 32 85 100 1(No Problem in Practical Use)

EXAMPLE 4

Metallized AlN substrate materials each of which had a high meltingpoint metallizing layer formed on an AlN substrate material by post-firemetallization and had the same size as that of sample 10 of Example 1were prepared, and intervening metal layers of different thicknesses of3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 40 μm and 50 μm were respectively formedon the high melting point metallizing layers by Ni—P plating. Thus, tensamples were prepared for each of these seven different thicknesses ofthe intervening layers.

Then, Cu plates of JIS C1020 each having a thickness of 0.3 mm and thesame length and width as the AlN substrate material were placed on therespective intervening metal layers of Ni—P, and the Cu plates werebonded to the respective intervening metal layers by heating underconditions similar to those of Example 1. The peel strength and the warpof each of the obtained samples were measured in a method similar tothat of Example 1, and defective portions were evaluated by an areaanalysis using an ultrasonic flaw detector. The results are shown inTable 7.

TABLE 7 Area Analysis by Ultrasonic Plating Peel Flaw Detector ThicknessStrength Warp Defective Sample (μm) (Kg/1 mm) (μm/mm) Portion (%) 33 30.6-0.9 1.4-2.0 14 (Practicable) 34 4 0.7-0.9 1.5-2.4  5 (Practicable)35 5 0.5-1.6 1.4-2.0  0 (Practicable) 36 8 1.5-1.7 1.6-2.3  0(Practicable) 37 10 1.4-1.8 1.3-3.3  0 (Practicable) 38 40 1.5-1.81.3-2.0  0 (Practicable) 39 42 1.7-1.8 2.6-2.9  0 (Practicable)

In addition, AlN substrate materials metallized by post-firemetallizing, each of which had the same size as that of the sample 10 ofExample 1 were prepared. The metallized AlN substrate materials weresubjected to Ni—P plating of 8 μm and sintered. 0.3-mm-thick Cu platesidentical to the aforesaid ones were bonded at a temperature of850-1000° C. by heating under conditions similar to those of Example 1.Evaluation similar to the aforesaid one was made on each of the obtainedsamples. The results are shown in Table 8. It can be seen from theresults that in the case of sample 44 exposed to a bonding temperatureexceeding the melting point of Cu, the Cu plate melted and no goodbonding was obtained.

TABLE 8 Area Analysis Bonding by Ultrasonic Tempera- Peel External FlawDetector ture Strength Warp Appear- Defective Sample (° C.) (kg/1 mm)(μm/mm) ance Portion (%) 40 880 1.6-1.8 1.3-1.6 Good 20 (Practicable) 41900 1.5-1.7 1.4-1.7 Good  4 (Practicable) 42 950 1.8-2.0 1.4-1.8 Good  0(Practicable) 43 1070 1.7-1.9 1.3-1.7 Good  0 (Practicable)  44* 1090Unmeasureable Cu melted (Unpracticable) (Note) The sample marked with *is a comparative example.

EXAMPLE 5

Metallized AlN substrate materials each having the same size as that ofsample 10 of Example 1 and a high melting point metallizing layer formedby a post-fire metallizing method similar to that used in Example 1 wereprepared. Thus, ten metallized AlN substrates were prepared for eachsample. Copper plates each having a bonding surface of the same size(length and width) as that at the substrate material and a thickness of0.3 mm were prepared separately from the metallized AlN substratematerials. After the bonding surfaces of the respective copper plates tobe bonded to the metallized AlN substrate materials were subjected toNi—B plating of 3 μm, Ni—P platings and Cu—Zn platings of variousthicknesses were formed, thereby forming intervening metal layers.

The intervening metal layers of some of the copper plates and themetallized surfaces of some of the AlN substrate materials were puttogether, and were bonded together under the same conditions asdescribed in Example 1 (samples 45 to 51). In addition, the othermetallized AlN substrate materials were subjected to the aforesaidplating, and the obtained products were respectively bonded to theabove-mentioned copper plates under the same conditions as set forth inExample 1 (samples 52 to 58).

The peel strength and the warp of each of the obtained samples weremeasured by a method similar to that of Example 1. The results are shownin Table 9 together with the results of observation of their externalappearances and the results of area analysis using an ultrasonic flawdetector. It can be seen from Table 9 that when the thickness of theintervening metal layer is controlled within the range of 3-40 μm, a farbetter bonding can be obtained, whichever side is covered with theintervening metal layer.

TABLE 9 Area Analysis by Ultrasonic Kind Plating Peel Flaw Detector ofThickness Strength Warp External Defective Sample Plating (μm) (kg/ 1mm) (μm/mm) Appearance Portion % 45 Ni-P 3 0.7-0.9 1.2-1.6 Good 20(Practicable) 46 Cu-Zn 4 0.6-0.9 1.4-1.7 Good 15 (Practicable) 47 Ni-P 52.0-2.4 1.3-1.6 Good  3 (Practicable) 48 Ni-P 8 1.9-2.3 1.2-1.7 Good  0(Practicable) 49 Ni-P 10 1.9-2.2 1.4-1.7 Good  0 (Practicable) 50 Cu-Zn30 1.8-2.1 1.2-1.6 Good  0 (Practicable) 51 Ni-P 42 1.9-2.2 2.6-2.9 Good 0 (Practicable) 52 Ni-P 3 0.6-0.9 1.2-1.7 Good 22 (Practicable) 53Cu-Zn 4 0.7-0.9 1.4-1.8 Good 17 (Practicable) 54 Ni-P 5 1.9-2.5 1.4-1.9Good  2 (Practicable) 55 Ni-P 8 1.7-2.2 1.4-1.6 Good  0 (Practicable) 56Ni-P 10 1.8-2.4 1.3-1.7 Good  0 (Practicable) 57 Cu-Zn 30 1.7-2.21.1-1.5 Good  0 (Practicable) 58 Ni-P 43 1.8-2.2 2.7-2.9 Good  0(Practicable)

Metallized AlN substrate materials each having the same size as sample10 of Example 1 and a high melting point metallizing layer formed by aco-fire metallizing method similar to that of Example 1 were prepared.Thus, ten metallized AlN substrate materials were prepared for eachsample. Copper plates having Ni—B platings and Ni—P or Cu—P platings, ofvarious thicknesses in a manner similar to that of Example 5 were bondedto the metallized AlN substrate materials via the intervening metallayers (plating layers) under the same conditions as set forth inExample 1.

Evaluations were made of the obtained samples in a manner similar tothat or Example 5. The results are shown in Table 10. It can be seenfrom Table 10 that effects similar to those of the samples fabricated bythe post-fire metallizing method of Example 3 were confirmed.

TABLE 10 Area Analysis by Ultrasonic Kind Plating Peel Flaw Detector ofThickness Strength Warp External Defective Sample Plating (μm) (kg/ 1mm) (μm/mm) Appearance Portion % 59 Ni-P 3 0.7-1.1 1.4-1.7 Good 20(Practicable) 60 Cu-P 4 0.9-1.4 1.3-1.9 Good 13 (Practicable) 61 Ni-P 53.1-3.6 1.6-1.8 Good  4 (Practicable) 62 Cu-P 8 2.9-3.4 1.3-1.9 Good  0(Practicable) 63 Ni-P 10 3.2-3.6 1.4-1.8 Good  0 (Practicable) 64 Cu-P30 3.0-3.2 1.5-1.6 Good  0 (Practicable) 65 Ni-P 42 3.0-3.2 2.6-2.9 Good 0 (Practicable)

EXAMPLE 7

Metallized AlN substrate materials each having a high melting pointmetallizing layer formed by post-fire metallizing under conditionssimilar to those of sample 10 of Example 1 were coated with an Ni pastecontaining 12 mole % of P by screen printing, and after the Ni paste wasdried in a belt furnace, Cu plates were bonded to the substratematerials under the same conditions as those of Example 1. Each of theobtained samples was evaluated in the above-mentioned manner. Theresults are shown in Table 11 according to the thicknesses of theintervening Ni—P layers. It can be seen from the results that even ifthe intervening metal layer is formed by a method other than plating, itis possible to achieve an effect similar to that of an intervening metallayer formed by plating.

TABLE 11 Ni Area Analysis Intervening by Ultrasonic Layer Peel FlawDetector Thickness Strength Warp Defective Sample (μm) (kg/1 mm) (μm/mm)Portion (%) 66 5 2.0-2.5 1.3-1.5 6 (Practicable) 67 8 1.9-2.4 1.5-1.8 0(Practicable) 68 10 2.1-2.6 1.4-1.7 0 (Practicable) 69 42 2.2-2.52.7-2.9 0 (Practicable)

EXAMPLE 8

A member of sample 10 produced by the co-fire metallizing method ofExample 1 and a member of each of samples 4-a and 4-b shown in Table 4,which were produced as the comparative examples, were bonded to aCu-made heat sink board by a eutectic solder, thereby fabricatingsemiconductor devices each having the structure shown in FIG. 3.

Specifically, the member of sample 10 is identical to the member 5having the structure in which, as shown in FIG. 4, the W high meltingpoint metallizing layer 2, the Ni—P intervening metal layer 3 and thecopper conductor layer 4 are bonded to both sides of the AlN substratematerial 1 in this order. This member 5 was bonded to the copper-madeheat sink board 6 by using a eutectic solder 7, and the semiconductorelement 8 was connected to the member 5 via the leads 9 by die-bondingin a manner known to those skilled in the art. Then, as shown in FIG. 3,the thus obtained product was accommodated into the casing 11 providedwith the external terminals 12 and the casing 11 was filled with theresin filler layer 13, thus fabricating a semiconductor device.

In the member of the comparative example, as shown in FIG. 5, as abonding layer 10 substituted for both the W high melting pointmetallizing layer 2 and the Ni—P intervening metal layer 3 of sample 10,an Ag solder layer and a W high melting point metallizing layer (sample4-a) or a Cu eutectic layer (sample 4-b) are (is) formed on each side ofthe AlN substrate material 1. The structures of the other parts of thecomparative example and the structures of semiconductor devices when thesemiconductor device elements 8 are mounted on these members are thesame as those of sample 10 of the present invention shown in FIGS. 4 and3.

Each of these semiconductor devices was subjected to a 1,000-cycle heatcycle test. In the semiconductor device provided with the member of thesample 10 of the present invention, no defect due to cracking or warpwas observed around the peripheries of the AlN substrate material 1 andthe Cu conductor layer 4. In contrast, in each of the semiconductordevices provided with the samples 4-a and 4-b, cracks running toward theAlN substrate material 1 were produced at the interface between the AlNsubstrate material 1 and the Cu conductor layer 4.

As is apparent from the above description, since the member according tothe present invention has a connection structure in which an interveningmetal layer is provided on an AlN substrate material provided with ahigh melting point metallizing layer and a conductor layer consistingmainly of copper is formed on the intervening metal layer, it ispossible to provide a semiconductor device which has a markedly highreliability compared to any of the conventional connection structures.In particular, the member of the present invention which has theaforesaid connection structure has a superior reliability as a memberfor high-power modules.

In accordance with the present invention, it is possible to providereadily and inexpensively a highly reliable member for a semiconductordevice, in which a metal member such as a lead frame made of copper,Kovar or the like is bonded to an aluminum nitride substrate materialwith high strength without cracking nor warp, preventing the substratematerial from suffering damage or deformation which would have beencaused by conventional bonding using soldering on a metallizing layer orcopper oxide eutectic when the metal member is mounted on a conventionalsubstrate material.

What is claimed is:
 1. A member for a semiconductor device in which ahigh melting point metallizing layer consisting essentially of not lessthan 80 volume % of at least one high melting point metal selected fromthe group consisting of W, Mo, Ta, Ti and Zr and not greater than 20volume % of glass frit, and an intervening metal layer which has ainciting point of not greater than 1,000° C. and consists essentially ofat least one member selected from the group consisting of nickel, copperand iron or a member selected from the group consisting ofnickel-phosphorous, nickel-boron, copper-zinc and copper-phosphorus areformed in this order on an aluminum nitride substrate material, and aconductor layer consisting essentially of copper is directly bonded as acircuit layer to said intervening metal layer, without forming anintervening solder layer, wherein said intervening metal layer is 2-40μm in thickness.
 2. A member for a semiconductor device, according toclaim 1, in which, in the end shape of said conductor layer, the angleformed by a bonding interface between said conductor layer and saidintervening metal layer and a side face of said conductor layer is notgreater than 80°, whereas the angle funned by the upper surface and theside face of said conductor layer is not less than 80°.
 3. A member fora semiconductor device according to claim 1, in which said high meltingpoint metallizing layer is 3-50 μm in thickness.
 4. A member for asemiconductor device according to claim 1, in which said interveningmetal layer includes two layers, a nickel-boron layer and anickel-phosphorus layer, formed in this order on said substratematerial.
 5. A method of manufacturing a member for a semi conductordevice, in which a conductor layer consisting essentially of copper isbonded to an aluminum nitride substrate material, the method comprisingthe steps of: coating a sintered aluminum nitride substrate materialwith a paste comprising at least one high melting point metal selectedfrom the group consisting of W, Mo, Ta, Ti and Zr and a glass frit, andfiring said paste to form a high melting point metallizing layerconsisting essentially of not less 80 volume % of the high melting pointmetal and not greater than 20 volume % of the glass frit; forming anintervening metal layer which has a melting point of not greater than1,000° C. and consists of at least one selected from the groupconsisting of Ni, Cu and Fe or a member selected from the groupconsisting of nickel-phosphorous, nickel-boron, copper-zinc andcopper-phosphorous, on either or both of said high melting pointmetallizing layer and a conductor layer consisting essentially ofcopper; and bonding said aluminum nitride substrate material to saidconductor layer consisting essentially of copper as a circuit layer viasaid intervening metal layer at a temperature of less than the meltingpoint of said conductor layer, without forming an intervening solderlayer, wherein said intervening metal layer is 2-40 μm thickness.
 6. Amethod of manufacturing a member for a semiconductor device, in which aconductor layer consisting essentially of copper is bonded to analuminum nitride substrate material, the method comprising the steps of:coating a compact comprising an aluminum nitride material powder with apaste comprising at least one high melting point metal selected from thegroup consisting of W, Mo, Ta, Ti and Zr and a glass frit, and thenfiring the body to obtain an aluminum nitride substrate material, thesame time, form a high melting point metallizing layer consistingessentially of not less than 80 volume % of the high melting point metaland not greater than 20 volume % of the glass frit; forming anintervening metal layer which has a melting point of not greater than1,000° C. and consists essentially of one selected from the groupconsisting of Ni, Cu and Fe, or a member selected from the groupconsisting of nickel-phosphorous, nickel-boron, copper-zinc andcopper-phosphorous, on either or both of said high melting pointmetallizing layer and a conductor layer consisting essentially ofcopper; and bonding said aluminum nitride substrate material to saidconductor layer consisting essentially of copper as a circuit layer viasaid intervening metal layer at a temperature of less than the meltingpoint of said conductor layer, without forming an intervening solderlayer, wherein said intervening metal layer is 2-40 μm in thickness. 7.A semiconductor device in which a semiconductor element is die-bonded tothe member for a semiconductor set forth in claim
 1. 8. A member for asemiconductor device according to claim 1, wherein the planar length andwidth of said conductor layer are shorter than those of said highmelting point metallizing layer and said intervening metal layer by notless than 0.05 mm.
 9. A member for a semiconductor device according toclaim 1, in which the planar length and width of said conductor layerare shorter than those of said high melting point metallizing layer andsaid intervening metal layer by not less than 0.05 mm.
 10. A member fora semiconductor device according to claim 1, in which said interveningmetal layer is made of nickel-phosphorus.